As displays combined with input means, display devices with touch panels are widely used in electronics, such as laptop computers, OA equipment, medical equipment, car navigation devices, portable electronic devices such as mobile phones, and personal digital assistants (PDAs).
Here, different types of touch panels are known, including capacitive type, optical type, ultrasonic type, electromagnetic induction type, resistance film type, and the like. Among these, in particular, capacitive type, which detects input coordinates by monitoring changes in the electrostatic capacity between a finger tip and a conductive layer, is becoming the mainstream of current touch panels, on par with resistance film type.
As a conventional display device with a capacitive touch panel, for example, a liquid crystal display device is known to have: a backlight-side polarizing plate; a liquid crystal panel formed with a liquid crystal layer sandwiched between two glass base plates (a thin film transistor base plate and a color filter base plate); a viewing-side polarizing plate; a touch sensor unit; and a cover glass layer, which are stacked in the stated order from the backlight side towards the viewing side. Additionally, the above conventional liquid crystal display device with a capacitive touch panel may have a phase difference film for viewing angle compensation provided between the liquid crystal panel and the viewing-side polarizing plate.
In addition, a conventional liquid crystal display device with a touch panel proposes providing a quarter wavelength plate between a viewing-side polarizing plate and a cover glass layer such that linearly polarized light traveling from the liquid crystal panel side through the viewing-side polarizing plate towards the cover glass layer side is converted by the quarter wavelength plate into circularly polarized light or elliptically polarized light (see, for example, JP2009-169837A (PTL 1)). In this way, when a liquid crystal display device with a touch panel is operated by an individual wearing polarized sunglasses, the displayed content can be visually recognized even under the condition of so-called crossed nicols, in which a transmission axis of the viewing-side polarizing plate and a transmission axis of the polarized sunglasses are set orthogonal to each other.
Moreover, as another conventional display device with a capacitive touch panel, an organic EL display device is known to have: a display panel formed by an organic EL display (OLED) panel and a barrier glass layer which is positioned closer to the viewing side than is the OLED panel; an anti-reflective circularly polarizing plate formed by a quarter wavelength plate and a polarizing plate which is positioned closer to the viewing side than is the quarter wavelength plate; a touch sensor unit; and a cover glass layer, which are stacked in the stated order from the display panel side (light emitting side) towards the viewing side (see, for example, JP2013-41566A (PTL 2)). Such an organic EL display device can prevent incident external light (natural light) being reflected at the surface of the OLED panel (particularly the surface of an electrode in the OLED panel) from making visual recognition of the displayed content difficult.
Additionally, any of the above conventional display devices with capacitive touch panels has a touch sensor unit that is formed with, for example, two transparent base plates, each having a conductive layer formed on a surface thereof, stacked together such that the conductive layer of one transparent base plate face a surface of the other transparent base plate on the side opposite where the conductive layer of the other transparent base plate is formed (see, for example, JP2013-3952A (PTL 3)).